Donald J. Trump and Pope Leo XIV are at it again, or at least the president is. This week in the continuing saga of the pope against the president, Mr. Trump suggested that Leo was a supporter of a nuclear-armed Iran, accusing him of “endangering a lot of Catholics.”

“I guess if it’s up to the pope, he thinks it’s just fine for Iran to have a nuclear weapon,” he told a conservative talk show host on May 5. This is not the first time Mr. Trump has made that allegation. He suggested the same during his first round with Leo in April.

Facing a press gaggle following the president’s remarks, Leo told reporters: “The church’s mission is to preach the Gospel, to preach peace.”

“If anyone wants to criticize me for proclaiming the Gospel, let them do so with the truth,” he said. “For years, the church has spoken out against all nuclear weapons, so there is no doubt about that. And so I simply hope to be heard for the sake of the value of God’s words.”

Not politics, but the Gospel

Archbishop John Wester leads the Archdiocese of Santa Fe, N.M., where the famed nuclear-weapons research site of Los Alamos is located. He has become one of the U.S. church’s leading figures on nuclear weapons disarmament and now abolition.

In this latest contretemps, he believes the president’s words betray misunderstandings of both the role of the pope and the church’s moral stance on nuclear weapons and nonproliferation.

“The president is not hearing what the pope is saying,” Archbishop Wester says. “He’s hearing through a different [filter].
 I think of the Scripture of ‘those that have ears to hear,’ and it doesn’t appear that the president has ears to hear.”

“The pope is not engaging in politics. He’s engaging in the Gospel.”

“Pope Leo’s been very clear that he’s against war, and he’s definitely against nuclear weapons,” Archbishop Wester said. He noted the pope’s prayer for peace on March 5 when he said: “Lord, enlighten the leaders of the nations, so they may have the courage to abandon projects of death, halt the arms race, and place the lives of the most vulnerable at the center…. May the nuclear threat never again dictate the future of humanity.”

The prayer was poignant and prescient, Archbishop Wester said. “We’re in a second arms race now that’s more dangerous than the first with A.I., hypersonic delivery systems and the geopolitical landscape that we are dealing with. The pope is right to be sounding the alarm and proclaiming the message of peace.”

Mr. Trump—and perhaps many American Catholics—may be surprised to discover how far the church has moved in recent years on moral questions related to nuclear weapons. Since St. John XXIII’s 1963 encyclical “Pacem in Terris,” the church has condemned the use of nuclear weapons as morally indefensible. Under Pope Francis, the church adjusted its teaching to assert that the possession of nuclear weapons, even as a deterrent against the aggression of another nuclear power, cannot be morally licit. The church has acted on that belief.

In July 2017, the Holy See voted in favor of a resolution to adopt a draft treaty forbidding states to “develop, test, produce, manufacture, otherwise acquire, possess or stockpile nuclear weapons or other nuclear explosive devices.” Months later, the Holy See was among the first nations to ratify the international treaty banning nuclear weapons.

“I am waiting for all of us to really take seriously Pope Francis’ challenge that even the possession of nuclear weapons is immoral,” Archbishop Wester said. The church had “carved out a space for deterrence,” but now “Francis has taken that off the table, and we know that deterrence in and of itself is not a strategy.”

The world has been lucky over the last 80 years to avoid a nuclear catastrophe, but “luck is not a strategy,” the archbishop said, quoting the late Robert McNamara, defense secretary under Presidents Kennedy and Johnson. Francis, and now Leo, have been “wise to sound the alarm, but no one’s listening. This latest dust-up that Trump has started demonstrates that clearly.”

An immoral and unnecessary ‘modernization’

Frustration has been building among peacemakers and arms-control advocates because of inaction on decades-old commitments toward nuclear disarmament. Progress has not only stalled on nonproliferation and disarmament; it is in acute danger of hurtling backward as major nuclear powers, including the United States, Russia, China and France, speak of massive investments in “modernizing” their nuclear arsenals.

In an assessment in April 2025—that is, before the Trump administration asked for a historic spike in defense spending for fiscal year 2027—the Congressional Budget Office projected that plans for the “modernization” of America’s nuclear weapons capacity by 2034 would cost $946 billion—an average of about $95 billion a year.

Those modernization programs are “immoral on many levels,” Archbishop Wester said, beginning with the simple reality that “if these weapons that they’re modernizing were ever used, it would be the end of civilization as we know it.”

The trillion-dollar price tag is another scandal before a world in need, the archbishop said. The poor and vulnerable “are being cheated because of the money spent on these nuclear warheads.” He added that the proposed new arms research and development is not even necessary to ensure the gruesome effectiveness of nuclear arsenals. More research and the creation of new weapons also represent huge calamities for the environment and communities near development sites.

“All these questions loom large, it seems to me,” Archbishop Wester said. “And they all point to the same thing—that we’re involved in a very immoral, ill-advised, irrational arms race that just doesn’t make any sense.”

On the same day the pope and the president duked it out in the press, a delegation from the Holy See addressed a meeting of the parties to the Treaty on the Non-Proliferation of Nuclear Weapons at the United Nations in New York. Msgr. Robert D. Murphy, the head of the Holy See delegation, expressed the Vatican’s continuing support for the peaceful use of nuclear energy and endorsed the vital role of the International Atomic Energy Agency in managing it. The I.A.E.A. is the international watchdog commission that was kicked out of Iran after Mr. Trump ripped up the Iran nuclear accord during his first term.

“The Treaty on the Non-Proliferation of Nuclear Weapons recognizes the inalienable right of all States Parties to engage in the research, production, and use of nuclear energy for peaceful purposes, provided they comply with their non-proliferation obligations,” Monsignor Murphy said in his address. The Holy See urged multilateral cooperation and oversight, stressed the need to avoid conflict near nuclear facilities and added its support to the development of peaceful nuclear technologies and sustainable and safe methods of addressing nuclear waste.

Reading the diplomatic subtext, the Holy See’s position on N.P.T. suggests that Iran, like all other nations, cannot be prohibited from developing nuclear technology for peaceful purposes as long as it agrees to do so responsibly and with multilateral oversight of the I.A.E.A. It additionally supports the Middle East as a nuclear weapons-free zone, a message to the region’s only nuclear-armed power, Israel.

The end of ambiguity

Israel maintains a policy of nuclear ambiguity, but it is believed to have at least 90 nuclear weapons in its arsenal. According to investigative reporters and arms control analysts, the state of Israel maintains what’s been called the Samson Option: If it were ever to find itself on the losing end of a conventional war, it would launch nuclear strikes at the population centers of its regional adversaries in an attack that just might obliterate everyone in the Middle East, much as Samson took his own life in a final act of strength and retribution that brought temple walls down on all of Israel’s enemies.

But does that last-option plan still remain a last option? Israel is by far the region’s superior conventional military power and has had little trouble in its sorties against Iran. But even as whatever existential threat Iran actually represents appears for now neutralized, talk of Israel’s first strike use of nuclear weapons is in the air.

On Polymarket, gamblers have been laying money down on the likelihood of an Israeli nuclear strike. Meanwhile, inquiring minds at the Bulletin of Atomic Scientists wonder if the Trump administration will beat the Israelis to it.

That kind of trickle-down doomsday chaos is precisely the reason Leo urged an end to the war, and it is among the scenarios that converted the Holy See into a supporter of abolition. “Pacem in Terris” condemned the use of nuclear weapons, but the encyclical failed to close a loophole that tolerated nuclear deterrence, the balance of terror maintained by the United States with Russia, but only as a stepping stone to the eventual total abolition of these apocalyptic weapons. That last bit has proved problematic. After years of inaction on disarmament, the Holy See has determined that the church’s condemnation of nuclear weapons had to include deterrence.

In Washington on May 5, 30 Democratic members of the House of Representatives released a letter addressed to Secretary of State Marco Rubio, demanding an end to Israel’s nuclear ambiguity and the pretense that the United States is unaware of Israel’s nuclear weapons capacity.

“The risks of miscalculation, escalation, and nuclear use in this environment are not theoretical,” the House members wrote. “American service members continue to be deployed throughout the region. Congress has a constitutional responsibility to be fully informed about the nuclear balance in the Middle East, the risk of escalation by any party to this conflict, and the administration’s planning and contingencies for such scenarios. We do not believe we have received that information.”

In defense of the nuclear nonproliferation regime, they asked Mr. Rubio to “hold Israel to the same standard of transparency that the United States expects from any other country that may be pursuing or retaining nuclear weapons capability.”

Archbishop Wester agrees that the time has come to speak more honestly about the realities of nuclear weapons in the Middle East and around the world. “Ukraine and Gaza, and now Iran and Lebanon and countless other places, sadly…demonstrate how easy it is for human beings to go down that slippery slope of war,” he said. “And if it’s ever [toward] a nuclear war, well, then that’s the end of it.”

Supporters of a ban on nuclear weapons have been dismissed as naive. Archbishop Wester wonders if the true naivete is to continue to live in a world that accepts nuclear weapons under the flimsy faith that they will never be used. “The human race has to wise up to the danger that we’re in,” he said.

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Kevin Clarke is America’s chief correspondent and the author of Oscar Romero: Love Must Win Out (Liturgical Press).